1. Field of the Invention
The present invention relates to disk drive performance features and more particularly to a disk drive having a cache control system for improving the disk drive's response time to host commands.
2. Description of the Prior Art
A host computer stores and accesses data on a disk drive by issuing commands to the disk drive over a standardized interface. The smallest indivisible data unit addressable on a disk is a logical block or disk sector, typically of 512 bytes, and each such disk sector is assigned a logical block address (LBA). When the host computer sends a command to the disk drive, the nature of the command is specified, e.g., read or write, along with a start LBA and a count specifying the number of contiguous sectors to be transferred.
Existing disk drives typically have a semiconductor cache memory for temporarily storing disk data that is likely to be requested by a host computer. The response time latency for storing and accessing data in a semiconductor memory is much smaller than the response time latency for mechanically storing and accessing data stored on a rotating disk. In existing disk drives, if the entire LBA range specified by a host command cannot be stored in a contiguous segment in the cache memory, then a sufficiently large contiguous segment in the cache memory must be allocated and configured for responding to the host command. The disk drive's response to the host command may be delayed while the contiguous segment is formed.
Accordingly, there exists a need for a disk drive having a disk cache architecture for efficiently configuring memory segments for effectively responding to host commands. The present invention satisfies these needs.